What is the general consensus of how close the inside edge of the air ducts fit to the cylinders? I've recently redone the intake seals, which with the older cowl and narrow ducts is quite tricky to get a good seal and retain the ability to remove the cowl , but I'd like to improve the fit along that inside edge. The problem with the narrow ducts on the 6 pot is the inside edge does not run parallel to the cylinder fins until about half way, this is more acute on the 2-4-6 bank. Meaning the from the middle cylinder forward the duct edge fits on top of the fins. I'm sure I can improve it with some silicone baffle seal or such like but was wondering how beneficial it would be.

In an ideal world, yo would have a perfect seal. However, that is almost impossible if you are using the standard Jabiru baffles. Have you tried using a thinner strip of rubber? Just as good, just easier to bend when putting onor removing baffles. Available from ebay:

weirdfish wrote:What is the general consensus of how close the inside edge of the air ducts fit to the cylinders? I've recently redone the intake seals, which with the older cowl and narrow ducts is quite tricky to get a good seal and retain the ability to remove the cowl , but I'd like to improve the fit along that inside edge. The problem with the narrow ducts on the 6 pot is the inside edge does not run parallel to the cylinder fins until about half way, this is more acute on the 2-4-6 bank. Meaning the from the middle cylinder forward the air duct cleaners portland oregon edge fits on top of the fins. I'm sure I can improve it with some silicone baffle seal or such like but was wondering how beneficial it would be.

I'm not convinced that the seal needs to be in any way perfect. I've spent many hours working on this on a J430.

I found that opening up the rear of the duct (at the very bottom rear of the duct) had the biggest results and allowed greater masses of air to flow through. Blow air into the duct at the front with an air compressor spray/blower type fitting and put your hand at the rear and see where the air escapes. Pull the rear of the duct away from the cylinder and you'll feel more air coming out - this is good. The theory of closing off all exists which will force air down between the cylinders doesn't hold water for my installation, it responds much better to increased flow.

I've posted pics of my ducts in another here somewhere.

As per my pics I also fitted "ramps" at the front of my ducts like perhaps an RV.